PORTLAND CEMENT TESTING. 171 



The American Society specifications, with some modifications, will 

 be adojated to test cement for all future Philippine construction work. 

 Although this change has been favored by this laboratory, we do not 

 believe that the above table, regulating the amount of water for mortar 

 briquettes, will be advisable in this climate. A natural, sie^■ed Philippine 

 sand will also be used, but the ratio between the results obtained with 

 this and those with standard Ottawa sand is still to be determined. 



Atmospheric influences will not. afEect the cement during mixing and 

 molding according to these specifications to as great an extent as with 

 the tamping method, as the whole operation of making the briquettes, 

 once the normal consistency has been ascertained, requires only about 

 one-third of the time. ^ 



However, the tamping method, according to the United States Arnry 

 specifications, is more in accordance with actual practice. It takes from 

 sixteen to eighteen minutes to gauge the molds, which is about the 

 average time that concrete manipulation in structural work requires. 

 If the cement begins to set in ten or fifteen minutes, the tensile strength 

 of the briquettes will be reduced by su.bsequent tamping, which is just 

 what may be expected to happen in field work. According to the 

 American Society manipulation, the briquettes are gauged in five or six 

 minutes, hence the result of quick setting ten or fifteen minutes after 

 the water is added does not affect the tensile strength so much, as the 

 intermingling of crystals which are then formed are not liroken up by 

 subsequent tamping. Therefore, failure to pass the initial set require- 

 ments of cements tested according to the American Society specifications 

 must be given more important consideration than otherwise, as the tensile 

 strength, while little afEected in laboratory tests, may suffer considerably 

 thereby in construction work. 



SPECIFIC GRAVITY AND LOSS ON IGNITION. 



Much diversity of opinion exists among cement workers regarding the 

 value of the specific-gravity test. It was formerly considered as an 

 almost infallible indicator of adulteration and underburning. The work 

 of Butler,-^ Meade,-* and of the committee on technical research of the 

 Association of Cement Manufacturers has proved that low specific gravity 

 is often due to seasoning, and that Portland cement can be heavily 

 adulterated and still retain a specific gravity above 3.10. As a result, 

 many engineers do not now attribute any value whatever to this test. 

 However, the experience of this laboratory induces us to support the 



=^Ghem. Emj. (1907), 5, 219. 

 -^Ghem. Eng. 6, 17. 



